Technology update

Jul 1, 2013

'Lattice plasmons' help make for new nanolaser

Researchers at Northwestern University in the US have developed a new room-temperature nanolaser based on metal nanoparticle arrays surrounded by a gain medium made of organic dye molecules. The device, which works using a new type of photon-plasmon excitation called a "lattice plasmon", could help in the development in next-generation information technology in which photons rather than electrons make up circuit components.

Reducing the size of photonic and electronic components will be crucial for a wide range of technological applications, from ultrafast data processing to ultradense data storage. Coherent nanoscale light sources, such as lasers, for their part, could also be useful for making optical devices that are small enough to beat the diffraction limit of light.

The new laser, designed by Teri Odom and colleagues, is made of gold or silver nanoparticles that act as nanolasing cavities. These cavities support localized optical fields that extend tens of nanometres from their surface. When these nanoparticles are arranged in a 2D array, they can then interact with each other to form a new type of photon-plasmon excitation called a lattice plasmon. Plasmons are collective oscillations of electrons on a metal surface.

Amplifying lattice plasmons

The cavities are surrounded by a gain medium made of the polymer polyurethane doped with dye molecules. At certain photonic states (the band edge ones), the lattice plasmons stop moving altogether and they can be amplified by stimulated energy transfer from photoexcited dye molecules in the gain via a distributed feedback mechanism to generate coherent laser light, explains Odom. Constructive interference of the amplified light allows light to be emitted perpendicular to the nanoparticle array surface at well-defined wavelengths. The direction of the emitted light beam is an important characteristic of a conventional photonic laser; however, most plasmon-based lasers made to date have only had poor beam directionality, until now.

The Northwestern team says that it would now like to look at changing the geometric structure of the individual cavities, as well as the distance between the cavities (the lattice periodicity). "We would eventually like to convert the 2D array structures into 3D ones," said Odom. "We are also interested in incorporating semiconductor gain materials into the nanolaser device so that it would work using electricity instead of just light."

The research should hopefully interest the photonics and laser communities, who are pushing the development of nanoscale components for optical circuits and the tiniest possible lasers that might be used for information processing in next-generation devices, she added.